MRI is a non-invasive technique with broad diagnostic value. The technique has gained wide clinical acceptance and is of great importance in diagnostic medicine. However, despite significant technological advancements (increasing field strength and improvement in technology), applications of MRI are limited by an intrinsically low sensitivity.
Some alternatives to enhance its sensitivity have been developed which involve ex-vivo nuclear spin polarisation of agents, prior to administration and consequent in-vivo MR signal measurement.
WO 99/35508 describes a method for obtaining hyperpolarized high T1 agents by dynamic nuclear polarization (DNP). Intermediate molecules of metabolic cycles, including amino acids, are mentioned among the hyperpolarized high T1 agents, which can be used for in vivo imaging of metabolic activity; amino acids are mentioned among these molecules.
WO 2009/098191 describes a method for preparing hyperpolarized amino acids which comprises preparing a DNP mixture (i.e. a mixture suitable for undergoing DNP) of carboxylate salts of the amino acid by admixing the amino acid with an aqueous solution of an alkali metal or earth alkali metal hydroxide.
The Applicant has however observed that when the above method is used for hyperpolarizing amino acids comprising an additional non-terminal amino group in the molecule (glutamine in particular), formation of undesirable by-products of said amino acids are observed in the DNP mixture.
The applicant has now found a new method for preparing a DNP mixture comprising glutamine, which substantially reduces or avoids the above drawbacks.